Nanoscience and Nanotechnology 2016, 6(1A): 65-67
DOI: 10.5923/c.nn.201601.12
TiO2 Nanotubes Decorated with Carbon Nanoparticles
for Indigo Carmine Photodegradation
Iasmim Biasi1, Janine H. Dias1, Melissa M. Rodrigues1,2, Hemerson P. S. Castro1, Tiago C. Severo3,*,
Daniel Weibel4, Célia de F. Malfatti2, Ricardo R. B. Correia1, Sérgio R. Teixeira1
1
Universidade Federal do Rio Grande do Sul (UFRGS), Programa de Pós-Graduação em Microeletrônica (PGMICRO), Brazil
2
Universidade Federal do Rio Grande do Sul (UFRGS), LAFOS, Instituto de Química, Brazil
3
Universidade de Caxias do Sul (UCS-CARVI), Centro de Ciências Exatas da Natureza e de Tecnologia, Brazil
4
Universidade Federal do Rio Grande do Sul (UFRGS), LAPEC, Departamento de Eng. Metalúrgica, Brazil
Abstract In this work we investigate the influence of Carbon nanoparticles on the photodegradation of Indigo Carmine
dye (ICD) using TiO2 nanotubes (TiO2NTs) decorated with Carbon nanoparticles as photocatalytic. For comparison we have
evaluated the ICD photodegradation using pure TiO2 as photocatalyst material. The Carbon nanoparticles have been
synthetized by laser ablation of graphite in ethanol and freestanding TiO2 nanotubes by anodization. The systems were
characterized by TEM, SEM, FTIR, XRD and Uv-Vis light absorption. The CNPs presented an average diameter around 3nm
with a remarkable broadband fluorescence under UV excitation. The TiO2NTs have a diameter average about 100 nm and
length around 4 µm.
Keywords Nanoparticles, Titanium dioxide, Indigo carmine, Solar photodegradation, Heterogeneous photocatalysis
1. Introduction
Indigo Carmine dye haspresented serious social and
environmental problems due to pollution of the environment
by industrial effluents. The waste produced often contains
toxic pollutants and it is resistant to conventional treatment
systems (coagulation/flocculation, adsorption on activated
carbon, precipitation, biological degradation among others).
[1] [2] The textile industry, in particular, has high demand
for water in its processes, generating large amounts of
wastewater, which, generally contains high loads of
dissolved salts, surfactants, suspended solids, and organic
matter, mainly in the form of complex dye molecules. [3-5]
Due to its complex chemical structure, when discarded into
the environment without any treatment, the dyes are not
easily biodegraded by bacteria present in the system,
remaining a long period in the ecosystem. [6] The Indigo
Carmine dye is highly toxic and may cause skin and cornea
irritations. It has carcinogenic properties that interfere with
neural development; and their consumption can be fatal. [7]
Fig. 1 shows the two structures in the dyes, noting the NaSO3
- Indigo Carmine group, which confers solubility in aqueous
environment. Fig. 1 also shows the chromophore group,
responsible for the dying of the color. This consists of a
* Corresponding author:
[email protected] (Tiago C. Severo)
Published online at http://journal.sapub.org/nn
Copyright © 2016 Scientific & Academic Publishing. All Rights Reserved
conjugated system with a substituted C = C bond by two
groups of the electron donor (NH)and two groups of electron
acceptors (C = O). [8]
Figure 1. Molecular structure of the dye indigo carmine
The development of efficient technologies for the
treatment of effluents containing dyes is a necessity, and
considerable efforts are dedicated to this field of research. In
the past few years the heterogeneous photocatalysis is been
researched due to its high efficiency in photobleaching of a
numerous of organic compounds at relatively low operating
costs. In this process, a semiconductor (photocatalyst) when
irradiated by equal or above band-gap energy which causes
the transfer of an electron of the valence band (BV) to the
conduction band (CB), forming a pair of electron-hole in
their surface charged by oxidation and reduction reactions of
the organic compounds. [9]
The synthesis of nanostructured semiconductors
represents a breakthrough for photocatalyst applications in
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Iasmim Biasi et al.: TiO2 Nanotubes Decorated with Carbon Nanoparticles for Indigo Carmine Photodegradation
the photodegradation of asolution containing the Indigo
Carmine dye because of the high surface area, and the rapid
electron-hole recombination. The semiconductor titanium
dioxide (TiO2) presents great interest because it is an
abundant material, cheap and highly chemically stable. On
the other hand, the TiO2 has limited photocatalytic activity
because of their band-gap (3.2 eV) and the rapid
recombination of a pair of electron hole generated by UV
radiation. [5] In this regard, the addition of NPs as carbon
quantum dots is a viable solution to increase the efficiency of
semiconductor in the photodegradation reaction of Indigo
Carmine dye. [10]
2. Methodology
To produce the fluorescent CNPs (carbon nanoparticles)in
ethanol by laser ablation method; we used a pulsed Nd-YAG
laser set at 1064 nm, operating at 20 Hz with energy about
100 mJ per pulse irradiating no focusing on solutions
composed by expanded graphite diluted in ethanol under
ultrasonic agitation during two hours. Lastly, this solution
was centrifuged in regime of 6000 rpm during 40 min to
separate the nanoparticles produced and the residual particles
from the initial solution, similar a method developedin [11].
The TiO2NTs were produced by anodization. The
anodization process is an electrolytic reaction that consists in
growing an oxide layer on a metallic substrate, with
addiction of Fluor ions at the electrolyte composition it is
possible to create some porous structures as well as
nanotubular geometries. As the electrolyte, we used a
solution composed by 0.5% wt NH4F (ammonium fluoride),
10% wt distilled water and ethylene glycol. The electrodes
were a titanium plate (99.98%) purchased from Sigma
Aldrish and cooper as a counter electrode. The syntheses of
the nanotubes were performed at room temperature in
ultrasonic bath without voltage slope during 1h, after this,
the thermal treatment was applied. Lastly, TiO2NTs (8 mg)
where added to CNPs solution (2 mL) with stirring for 10
min and dried in a vacuum oven at 80ºC for 12h.
The tests of photodegradation of Indigo Carmine were
conducted using a 30 ml quartz reactor. The reactor is
exposed to a solar simulator that comprisesa lamp of the
Xe/Hg of the 240W. The photocatalytic activity of the
photocatalysts prepared was evaluated by the percentage of
disappearance of Indigo Carmine via UV-Vis, based on the
absorption band at 611 nm.
3. Characterization and Discussion of
Results
The transmission electronic microscopy TEM and high
resolution HRTEM was employed to observe the
morphology and crystalline structure of the produced
nanoparticles. Those analyses reveal that the CNPs have a
size distribution around 3 nm diameters and the crystalline
structure of the C-dots with the distances of the patterns in
agreement with the (002) plane of the carbon graphite
structure. To understand the nature of bonds and to analyze
the composition of the CNPs surface, we measured the FTIR
spectra for the solvent and the colloids. Under UV excitation
the C-Dots displayed a great fluorescence. To measure the
fluorescence spectra was employed the following setup: a
pulsed (8 ns) Nd-YAG Laser set at 355 nm irradiated the
samples in a quartz cuvette, the fluorescence signal was
detected by a SM-240 Spectrometer coupled with an optical
fiber perpendicular to excitation beam. By XRD analysis, we
observed that TiO2NTs were in anatase phase. With the
CNPs attached on the TiO2NTs surface we have performed
the Uv-Vis light absorption spectra and compared to the pure
TiO2, presenting a yellow-brown coloration due to the CNPs
absorptionon UV and IR regions.
The result of photobleaching Indigo Carmine proved to be
excellent. In just one hour of irradiation, the
photodegradation of the Indigo Carmine, using the
TiO2NTs/NPCs as catalysts, was complete. The
photodegradation percentage of Indigo Carmine obtained
was 100%. When used only the TIO2NTs as catalyst, the
result of photodegradation of the dye was 95% in only 1-hour
exposure to the solar simulator.
4. Conclusions
According to the results presented, it was observed that the
developed photocatalysts were excellent when used on the
photodegradation of Indigo Carmine. Also, it was found that
the addition of CNPs in the TiO2NTs improves the
fotodegradation efficiency.
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Nanoscience and Nanotechnology 2016, 6(1A): 65-67
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